Resistance unit



Dea-4, l-92& l 1,693,825

E. R. STOEYKLYE RESISTANCE UNIT Filed ual-h 2e, 1925y Run-nner. m Oms RxsIs-rANcz m Oum INVEVTOR. Ami/n 3.3

A TTORNEY Patented '4, 19128. y

[INT1-IED STATES.

vPATENT OFFICE.

EBWIN B. STOEKLE, 0F MILWAUKEE, WISCONSIN, v'.ASSIGNOR TOTHE CUTLER-HAM- MER MFG. C0., 0F MILWAUKEE, WISCONSIN, A CORPORATION WISCONSIN.

' RESISTANCE UNIT.

Application led March 26, 1925. Serial No. 18,389.

This invention relates to resistance units, and more particularly to units havingarelatively large negative temperature coeicient of resistance.

In certain devices, such as automatic motor -starters and in relays for farm lighting systems, it is desirable to include relatively high resistance' in circuit initially and to automatically and rapidly decrease such resistance.

An object of this invention `is toA provide a resistance unit having characteristics such as to lnsure the aforementioned desirable results.

Another'object is to provide an' improved material having a large negative temperature in a flame or furnace will produce a result` ant mass of any desired resistance, depending upon the proportions ,of the respective ingredients; whereas by suitable proportioning a material may be obtained having a negative temperature coefficient of resistance such that the resistance thereof Will changel 300 to 400 per cent with a temperature change of 7 5 degrees C.

- An enamell suitable for present purposes may comprise the following ingredients:

Parts by weight Red lead 228 Zinc oxide 80 Raw kaolin 1 y 35 Boric' acid c y126 `and the material may be reduced to the de-l sired form by grinding it in a ball mill. Tov

a given quantity ofthis materialI mayaddan equal amount byweight of iron 'filings' or rent-resistance characterlstics of a device iron oxideto-produce, a mixture which is soft n and plastic at 500 600 degrees C. andows at 1000 degrees C. If the metal is introduced in the form of an oxide, a small amount of carbon should be mixed therewith so that under the heat treatment imposed the oxide will. be reduced to metallic form.

While I have mentioned an enamel hav` ing a-particular composition it Will be understood that other suit-able types of enamel, or even certain forms of low. melting point glass may be employed; Whereas copper or other suitable metals or their oxides may by substituted for that recited in the foregoing example.

I have devised a resistance unit utilizing the aforedescribed material which has the characteristic of reducting its resistance due to the heating effect of the current passing through it,-that is to say;l a negative temperature-resistance characteristic. One form of this unit is illustrated in Fig. 1 of the accompanying drawing:

2 illustrates a modified form of resistance`unit, and Y Figs. 3 and 4 show the current-resistance and temperature-resistance curves of given units constructed in accordance with Figs. 1 and 2, respectively.' f

Asillustrated in Fig. 1 a single coil 10 of` resistance Wire is Woundupon a tubular base 11 of porcelain or other suitable material. The opposite ends 12 and 13 of coil 10 are attached to conductors 14 and 15 in any suitable manner, as by soldering or brazing the former at points 16 and 17 to loops 18 and 19 ofthe latter, the batse llbeing provided With annular grooves 20 and 21 to receive said loops. The coil 10 is then coated with a layer 22 of the aforedescribed high temperature coeicient of resistance material. This coating ma'y be applied by moistening the 9 pulverized mixture With Water and plastering it over the winding. The unit is then heated to about 100() degrees C. 1n a furnace,

so that the'constituents of the coating matei rial are fused together to form a solld mass.

If desired, the surface of the coating may be smoothed With a piece of graphite While the material is still in a plastic state. Upon cooll ing, the coating material isvin the form of a stony mass having a dull grey metallic lustre. It does not crack or check, 'even when repeatedly heated and cooled? In'Fig. 3 the curve 23 illustrates the curcon/str'ucted in accordance with Fig. 1 hav-v ing a winding of 500 ohms resistance before coating,.and having a coating comprising equal parts by weight of iron filings and enamel, as heretofore described. The curve 24. in Fig. 3 illustrates the temperature-resistance characteristics of the same unit.

In the modified forni of unit illustrated in Fig. 2, thetubular insulating base 11 is Y provided with two separate windings 25 and 26, the coils o'which areparallel -to but spaced from each other on said base. One end of the winding 25 leads olf, as indicated at 27, whereas the other end thereof is provided, with a loop 28 engaging the groove 21 in base 11. Similarly, the wmding 26 leads olf, as indicated at 29, whereas the other endthereof is looped at 30 within groove 20. The coils 25 and 26 are coated with a layer 22 of the' resistance materialin the manner described in connection with Fig. 1.

The current-resistance and temperatureresistance curves of a device constructed in accordance with Fig. 2 are illustrated at 31 and 32, respectively, in Fig. 4. As indicated by said curves, the device of Fig. 2 provides a comparatively low initial resistance which, moreover, decreases rapidly. This low to be limited to the particular embodiments -of my invention shown herein, which merely indicate the broad range of applicability l of the invention.

What I claim and desire to secure by Letters Patent is:

1. A-resistance unit comprising a resistance i winding and a body of normally slightly conductive resistance material adapted to embed the same, said material comprising a mixture of finely divided' iron and afinely divided vitreous substance in jointly fused condition.

`2. A resistance unit comprising a windin of predetermined resistance, the coils of sai winding being embedded in a resistance material consisting of substantially equal parts of. a metallic substance and an enamel composed of red lead, zinc oxide, raw kaol'in and boric acid. v

3. A resistance unit comprising al winding of predetermined resistance, said winding being embedded in a fused compound consisting Y of equal parts of iron filings and an ename said enamel having ingredientsin the following proportions by-weight:

Red iena-; eas Zinc voxide 80` Rawrkaolin 35 Boric acid 126 4.. A resistance unit comprising a tubular insulating core, a resistance wire Wound thereabout, and a body of normally slightly conductive resistance material surrounding said Wire and embedding the same, said resistance material having va. negative temperature coetlicient of resistance and comprising a mixture of substantiallyequal parts of iron filingsand a finely divided vitreous enamel in jointly :tused condition.

5. A resistance unit comprising an insulat` ing core, a plurality of resistance wires wound thereabout, the coils of said Wires being ar-` ranged in parallel spaced relation to Ieach` other throughout the lengththereof, and'abody oftnormally slightly conductive resistance material surrounding said coils and embedding the same, vsaid resistance material having a negative' temperature coeflicient of resistance and comprising a mixture, in predetermined proportions,`of iron filings and a finely divided vitreous enamel in ointly fused condition.

In witness whereof, vlf have hereunto subscribed ymy name. v

ER W IN R. STOEKLE. 

